There has long been known a method of producing riboflavin by culturing riboflavin-producing microbes in a culture medium, forming and accumulating riboflavin therein and collecting riboflavin therefrom. As the riboflavin-producing microbes, there have also been known to use Eremothecium ashbyii, Ashbya gossypii, Candida flareri, Mycocandida riboflavina, Clostridium acetobutylicum, as well as to use Bacillus riboflavin-producing microbes (Japanese Unexamined Patent Publication (Kokai) No. 66894/1974), variable strains of Streptomyces testaceus (Japanese Unexamined Patent Publication (Kokai) No. 116690/1975), Achromobactor riboflavin-producing microbes (Japanese Unexamined Patent Publication (Kokai) No. 54094/1977), Previbacterium riboflavin-producing microbes (Japanese Unexamined Patent Publication (Kokai) No. 110897/1977), Saccharomyces riboflavin-producing microbes (Japanese Unexamined Patent Publication (Kokai) No. 241895/1985), Candida phamata (ATCC 20849) (International Patent Publication No. 509221/1993).
As the carbon sources in the culture medium, there have further been known to use saccharides such as glucose and sucrose, starches or hydrolyzed products thereof, acetic acid, citric acid, ethanol, or hydrocarbons and benzoic acid for certain kinds of microorganisms.
However, when oils and fats are used as carbon sources, oils and fats must be dispersed in an aqueous culture medium. For this purpose, the culture medium must be stirred, or a dispersant or an emulsifier must be added into the system.
Under the stirring conditions where the oils are emulsified or suspended in water, however, it is confirmed that the microbes themselves are killed and destroyed resulting in a decrease in the yield of riboflavin.
According to the method of adding the dispersant or the emulsifier into the system, further, the microbes are inevitably and adversely affected by these drugs and, besides, the added drugs mixes into the riboflavin that is formed.